Process for extracting dissolved methane from hydropressured aquifers

ABSTRACT

One undeveloped alternative fuel is methane dissolved in ground water. Equipment for extracting methane from ground water is readily available. This Application presents a process to produce and use dissolved natural gas in the United States. The process includes the use of production wells, pumps, gas/water separators, compressors, low pressure gathering lines, and water disposal wells. Dissolved methane is present in virtually every basin now known to produce oil and dry gas. The Great Valley of California alone contains undeveloped dissolved methane resources of about 1,200 trillion cubic feet (TCF). Dry gas production in 150 years was about 10 TCF. The first full scale test of the extraction process was completed on Jul. 7-8, 2010 in California. Laboratory analyses of the gas produced showed that it was equal in heat value (about 940 to 975 BTU per cubic foot) to dry gas produced from the same field.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

There are no parties associated with Gary F. Player or any other entity that have a joint research agreement with Gary F. Player.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

No sequence listings, tables, or computer programs have been submitted on compact discs. There are zero (0) compact discs submitted with this Patent Application.

BACKGROUND OF THE INVENTION

1. Technical Field

Natural gas production from porous and permeable sedimentary rocks.

2. Background Art

Natural gas prices are subject to market spikes far beyond the control of the largest company or agency. Energy costs in the United States can be freed from the demands of the world petroleum marketplace. One undeveloped replacement fuel is methane dissolved in ground water. This gas is present throughout the sedimentary basins of the world, just a few hundred meters below the surface of the ground. Dissolved methane resources in the United States are sufficient to replace the use of other fossil fuels for hundreds of years.

BRIEF SUMMARY OF THE INVENTION

All necessary equipment for extracting methane from ground water is readily available. However, until this Patent Application, no one had devised an economical method for combining modern technologies to harvest, store, and use dissolved gas in the United States. The apparatus includes:

1. Wells that will be drilled to depths of 1,000 to 5,000 meters below ground level in “hydropressured” sedimentary basins.

2. Low pressure, high capacity, pumps for lifting ground water from the wells and transporting it through pipes to treatment facilities.

3. Conventional, oilfield style gas/water separators for removing methane from the produced water at surface temperatures and pressures.

4. Low pressure, high capacity gas compressors.

5. Low pressure gathering lines to move the compressed methane to existing natural gas pipelines.

6. High pressure compressors for injecting methane into existing natural gas pipelines.

7. Injection wells for accepting injected waste water from the separators, constructed into the same highly permeable saline aquifers.

BRIEF DESCRIPTION OF FIGURE ONE

Figure One is a conceptual drawing showing the process developed to separate dissolved methane from hydropressured ground water showing each step in the extraction of methane.

BRIEF DESCRIPTION OF FIGURE TWO

Figure Two is a chart plotting the likely range of gas/water ratios (GWR) for gas dissolved in 0.9 molar Na Cl ground water, versus the depth below ground level.

DETAILED DESCRIPTION OF THE INVENTION

Rates of Methane Extraction

With an assumed dissolved methane concentration of about 15 cubic feet per barrel at 1,000 meters (a little more than 3,000 feet) below ground level, a water production rate of 500 gallons per minute from one well would provide 257 thousand cubic feet (MCF) of gas per day.

Production of 20,000 gallons of water per minute from a field of 40 wells would provide about 10.3 million cubic feet (mmcf) of gas per day. A field of 100 wells could produce 25.7 million cubic feet per day. Gas water ratios in excess of 23 cubic feet per barrel are common below 2,000 meters (about 6,700 feet) below ground. Gas production from 100 wells drilled to 2,000 meters and produced at the given water rates would be 39.4 million cubic feet per day.

Dissolved Methane Resources

Dissolved methane is present in virtually every basin now known to produce oil and dry gas. A typical example is the Great Valley of California. About 10 trillion cubic feet (TCF) of gas have been produced from the basin to date. Potential dissolved methane resources are much greater. The Great Valley has an area of at least 20,000 square miles, or 12,800,000 acres. Thousands of drilled wells have shown that at least 2,000 feet of permeable, hydropressured sandstones are present from 3,000 to 8,000 feet below ground level. That thickness of sandstone throughout the basin with a known average porosity of 30 percent, and an average gas/water ratio of just 20 cubic feet per barrel, would provide an undeveloped dissolved methane resource of about 1,200 TCF in one basin in just one state.

That volume of undeveloped dissolved methane is 120 times the cumulative California gas production in the last 150 years Similar quantities of dissolved methane occur in petroliferous basins across the United States, awaiting development.

The first full scale test of the extraction process was completed on Jul. 7-8, 2010 at the Gill Ranch Gas Field in Madera County, California. Dissolved gas and water were produced from hydropressured sands in the Santa Margarita and Zilch formations through perforated casing from about 3,140′ to 3,170′ feet below ground level (BGL). Due to open hole behind the casing wall, water from that interval was diluted by water from sands as shallow as 690 feet BGL, but gas was successfully separated from the water and burned in a flare for 16 hours. Laboratory analyses of the gas showed that it was equal in heat value (about 940 to 975 BTU per cubic foot) to dry gas produced from deeper zones at Gill Ranch.

Numbers on Figure One are defined as follows:

(1) Production Wells(s)

One or more wells will be needed to produce 500 gallons or more per minute of deep, methane-saturated ground water into the separators. The number and capacity of the well(s) will be based on the production rate needed for available markets.

(2) Separator(s)

Ground water will be pumped to the surface into oilfield style atmospheric pressure gas/water separators. Methane will be piped out the top, and water will be drawn out the bottom and returned to the ground through injection wells.

(3) Spent Water Injection Well(s)

Once dissolved methane has been recovered from ground water, the “spent” produced water will be injected back into the same aquifer. This step is necessary for three reasons:

I. The water will be saline and disposal will be carefully regulated by Federal, state, and local agencies;

ii. Local hydrostatic pressures in the aquifer will be reduced by nearby dissolved gas production wells, thereby reducing the energy required to pump the water back into the ground; and

iii. Replacement of the water will minimize permeability reduction in the aquifer that could be caused by lowering water pressures and allowing individual loose sand grains to settle and compact more closely together.

(4) Low Pressure Gas Compressor(s)

Methane will be recovered from the separators at or near atmospheric pressure. The gas must then be compressed for transport. Likely gathering line pressures will be about five (5) atmospheres so that the lines can be built with low strength materials. Gathering lines may be constructed of ABS or PVC plastics. The lines should be at least six (6)inches interior diameter, so that large quantities of gas can be stored per given distance.

(5) High Pressure Compressors(s)

Most regional trunk lines receive gas at about 750 to 1,000 pounds per square inch (more than 60 atmospheres). Gas delivered in low pressure gathering lines will be compressed as needed for injection into the high pressure trunk line(s) for shipment to market.

The vertical scale of Figure Two is depth below ground, with the depth in feet shown on the left-hand vertical axis, and depth in meters shown on the right-hand vertical axis. The horizontal axis shows the quantity of dissolved methane gas in cubic feet per barrel of produced water (42 gallons per barrel). Two sloping diagonal lines present predicted and observed values of dissolved natural gas in saline ground water. The sloping diagonal line on the left shows estimated concentrations of gas in ground water published by Culbertson and McKetta in 1951. The sloping diagonal line on the right shows measured concentrations of gas in ground water containing Na Cl published by Duan and others in 1992. A circle below 3,000 feet shows the observed concentration of dissolved gas reported by Paul Jones in 1978 from a well with hydropressured aquifers along the coast of the Gulf of Mexico. 

I claim:
 1. A method of dissolved natural gas production from wells having a well-bore, casing, tubing, and wellhead, which are drilled into hydropressured, gas-saturated saline aquifers, comprising the steps of: (a) pumping hydropressured water and associated dissolved gas to the surface; (b) separating dissolved gas from produced water with a conventional gas/water separator; (c) capturing the separated natural gas and compressing it for transport in pipelines; (d) injecting produced water back into the aquifer from which it was extracted.
 2. The method of claim 1, wherein step (a) further comprises: (I) completing production wells with slotted casing and gravel filter packs across thick (300 feet to 500 feet) net aquifer sand intervals; (ii) pumping dissolved gas and water to the surface with positive displacement, rod driven, “top-drive” submersible pumps, or (iii) utilizing high pressure gas flowing in small diameter “tremie” pipes to lift dissolved gas and water to the surface.
 3. The method of claim 1, wherein step (d) further comprises: (I) reinjecting produced water into the same hydropressured aquifer to maintain reservoir properties, including porosity and high permeability (1,000 to 3,000 millidarcies) in the aquifer sands or sandstones.
 4. The method of claim 3, wherein step (I), by preserving reservoir properties, will allow each production well to produce dissolved natural gas for 30 years or more with no decline in the ratio of gas production to water production.
 5. The method of claim 4, wherein dissolved gas concentrations in partially depleted aquifer sands will be replenished within hydropressured aquifers naturally by diffusion, thereby assuring long-term productivity of each dissolved gas production well. Inventor: Gary Farnsworth Player 